Manual Section... (2) - page: msync

NAME

SYNOPSIS

DESCRIPTION

msync()
flushes changes made to the in-core copy of a file that was mapped
into memory using
mmap(2)
back to disk.
Without use of this call
there is no guarantee that changes are written back before
munmap(2)
is called.
To be more precise, the part of the file that
corresponds to the memory area starting at
addr
and having length
length
is updated.

The
flags
argument may have the bits
MS_ASYNC,
MS_SYNC,
and
MS_INVALIDATE
set, but not both
MS_ASYNC
and
MS_SYNC.
MS_ASYNC
specifies that an update be scheduled, but the call
returns immediately.
MS_SYNC
asks for an update and waits for it to complete.
MS_INVALIDATE
asks to invalidate other mappings of the same file
(so that they can be updated with the fresh values just written).

RETURN VALUE

On success, zero is returned.
On error, -1 is returned, and
errno
is set appropriately.

ERRORS

EBUSY

MS_INVALIDATE
was specified in
flags,
and a memory lock exists for the specified address range.

EINVAL

addr
is not a multiple of PAGESIZE; or any bit other than
MS_ASYNC | MS_INVALIDATE | MS_SYNC
is set in
flags;
or both
MS_SYNC
and
MS_ASYNC
are set in
flags.

ENOMEM

The indicated memory (or part of it) was not mapped.

CONFORMING TO

POSIX.1-2001.

This call was introduced in Linux 1.3.21, and then used
EFAULT
instead of
ENOMEM.
In Linux 2.4.19 this was changed to the POSIX value
ENOMEM.

AVAILABILITY

On POSIX systems on which
msync()
is available, both
_POSIX_MAPPED_FILES
and
_POSIX_SYNCHRONIZED_IO
are defined in <unistd.h> to a value greater than 0.
(See also
sysconf(3).)